1. Field of the Invention
The invention relates to an overload protection device, more particularly to an overload protection device which has a relatively fast response time, which is not easily susceptible to erroneous operation due to the presence of noise, and which is capable of automatically closing a current-carrying circuit upon detection that the overload condition has elapsed.
2. Description of the Related Art
Conventional overload protection devices, such as fuses and non-fuse breakers, provide protection against excessive currents. In fuses, a fusible metal strip melts when the current therethrough exceeds the rated value for a definite time, thereby opening a current-carrying circuit. Non-fuse breakers, on the other hand, may be thermal or electromagnetic devices which open a current-carrying circuit automatically when the current therethrough exceeds a predetermined value.
The main drawbacks of conventional overload protection devices reside in their relatively slow response times and their susceptibility to erroneous operation due to the presence of noise. Thus, conventional overload protection devices are unsuitable for use in highly-sensitive equipments.
Another drawback of conventional overload protection devices is that they must be replaced (in case of fuses) or reset automatically by operating a lever (in case of non-fuse breakers) in order to close a current-carrying circuit. Therefore, it would be desirable to have an overload protection device which can close automatically a current-carrying circuit upon detecting that the overload condition has elapsed.